The determination of directions, angles and lengths as positions is required in many fields of use, such as, for example, in geodetic or industrial surveying. Developments in angle measurement technology lead via mechanical reading processes to fully automated angle measurement according to the prior art today.
Known scanning methods are electronic-magnetic, electronic and optoelectronic methods. The following statements relate to optoelectronic scanning devices.
Customary optoelectronic angle sensors for determining a rotational angle about an axis have a code carrier and an optical detector which are rotatable relative to one another. The optical detector is, for example, a photodetector, a CCD line array or a CCD area array. The code carrier is in general in the form of a circular disc or in the form of a circular ring and carries, along its circumference, an optically detectable position code, of which a section is mapped onto the detector by an illumination device. In general, the code carrier of the angle sensor rotates. However, it is also possible for the code carrier to be stationery and the detector to rotate.
For determining, for example, angular positions from 0° to 360°, the coding can be arranged in a full circle and can have, for example, dark and light regions. The angular resolution of the full circle is determined by the type of coding and by the scanning device used for reading the coding. Thus, for example, the angular resolution is increased by applying a code in a plurality of tracks or by a finer division of the code, the achievable resolution being limited for reasons relating to manufacture and cost.
US 2002/0018220 A1 discloses a measuring apparatus for determining a displacement of a code carrier, a detector film comprising organic photodetectors and organic transistors being applied as a detector above the code carrier which can be displaced relative thereto and has a readable code. For illumination and production of an image of the code, a luminescent film comprising organic LEDs is arranged behind the detector film, which luminescent film illuminates a part of the code and thus produces an evaluable image thereof on the detector film.
Luminescent films have long been known. They are also used, for example, for display illuminations, or thin-film transistor displays or as graphic elements for advertising purposes and have, for example, a multiplicity of organic LEDs, these being producible cheaply and in large quantities.
Known disadvantages of angle sensors of the prior art are a complex arrangement of the detector, of the code carrier and of the illumination device which is to be effected with high precision, the detector and the illumination device usually being arranged in each case on a separate circuit board to be supplied with power. One possibility for realising a simpler design and for reducing the number of circuit boards supplied with electric power is an arrangement of the illumination device and of the detector on a common circuit board, an image of the code which is dependent on the rotational position therefore being projected onto the receiving regions of the detector by a code carrier in the form of deflection means, which is disclosed, for example, in U.S. Pat. No. 7,145,127 B2.
Expensive and continuous computational reprocessing of the data determined from the image of the code for determining the angular position is also required for eliminating errors and inaccuracies known in the case of angle sensors of the prior art, such as, for example, out-off-true running of the code carrier. Alternatively, efforts are being made to counteract such errors and inaccuracies by means of hardware, for example by adjusting mechanisms for precise positioning of the code carrier, which, however, prove to be very expensive. Thus, for accurate angle measurement according to the prior art, the components used for this purpose generally have to meet high requirements with regard to their precision in manufacture and assembly.
Furthermore, a disadvantage of codings—owing to a resolution or fineness thereof—is that, once they have been manufactured and installed in an angle sensor, they have a specific accuracy with which angular position can be determined on the basis of the respective coding. Furthermore, an incremental coding can be read only up to a limited rotational speed, depending on its resolution. If coarse codings having a lower resolution are used, an angular position can be tracked and determined even during fast rotational movements of the code carrier but the achievable accuracy is lower than in the case of codings having a high resolution.